Method of making self-locking nut

ABSTRACT

Disclosed herein are prevailing torque type self-locking nut comprising a one-piece nuts each body having an internal screw thread surmounted by a well portion having an internal surface spaced from the thread axis a distance greater than one-half the major thread diameter, and a thin-walled self-locking element of thread impressionable thermoplastic material at least partly in the well portion and having an external surface secured by adhesion to the internal surface of the well portion and an internal surface spaced from the thread axis a distance less than one-half the major thread diameter. Also disclosed herein are a method of making such nuts, the method involving melting powder of the thermoplastic material in situ in the nut body, a pin useful in carrying out the method and nut body components of the self-locking nuts.

RELATED APPLICATION

This is a division of application Ser. No. 884,638, filed Mar. 8, 1978,now U.S. Pat. No. 4,282,913 which issued Aug. 11, 1981, whichapplication was a continuation-in-part of now abandoned application Ser.No. 781,485, filed Mar. 25, 1977.

BACKGROUND OF THE INVENTION

This invention relates to a method of making self-locking nuts of theprevailing torque type, in which the locking characteristic is providedby thermoplastic material.

Sauer U.S. Pat. No. 2,450,694, granted Oct. 5, 1948, discloses aprevailing torque type self-locking nut (hereinafter sometimes "theSauer nut") comprising a one-piece metallic nut body having a threadedbore portion, a first end of which is adapted to be entered by a matingexternally threaded member. At a second end of the threaded bore portionis an annular recess or well formed in part by a circumferentiallycontinuous annular flange portion extending axially away from the firstend. The flange portion includes a cylindrical surface coaxial with andconfronting the axis of the threaded bore portion. The Sauer nut alsoincludes a pre-formed nylon collar mechanically held in the recess. Theflange portion is crimped to engage the upper surface of the collar,thus to retain the same in the recess and prevent the same from turningrelative to the body. The collar has an internal cylindrical surfaceconfronting and coaxial with the thread axis and having a diameter whichis somewhat less than the major thread diameter, so that continuedrotation of the externally threaded member, after it traverses thethreaded bore portion, will cause it to engage the cylindrical surfaceof the collar to impress a thread therein and achieve the desiredself-locking effect, all is known fashion.

The pre-formed collar of the Sauer nut has a radial thickness which isquite large, thus imposing certain limitations on the overall dimensionsof the nut, which limitations are in certain cases undesirable, as willbe more fully explained hereinafter.

The Sauer nut has long been, and continues to be, preeminent amongprevailing torque type self-locking nuts.

However, for many years it has been evident that it is highly desirableto develop a new self-locking nut which is capable of being manufacturedat a significantly reduced cost relative to that of the Sauer nut butwhich is at least as good as the Sauer nut as to all significantperformance criteria.

The present invention has culminated the search for such a new nut.

The nut of the present invention can be made at a substantial reductionin cost relative to the Sauer nut, and is at least as good as the Sauernut as to all significant performance criteria.

In addition, as noted, the manufacture of the Sauer nut entails crimpingof the flange portion after the collar has been placed in the recess.This has two disadvantages. One, there is a limit to the hardness andhence ultimate tensile strength of the Sauer nut, as any heat treatmentto develop that strength must be accomplished before the collar isplaced in the recess and hence before the crimping operation. Also, thenut body blank of the Sauer nut cannot be cold formed of high workhardenable material. Two, in the Sauer nut, the crimped flange portionoverlies and extends axially beyond the collar, thus contributing to theoverall height of the nut without contributing to its locking ability orstrength.

The present invention avoids the crimping operation and in fact does notinvolve any metal working operation after the formation of the nut body.Hence, with the present invention, the nut body may be heat treated toany desirable hardness, and hence strength, thus making it possible toachieve a nut of improved strength-to-weight ratio with respect to theSauer nut.

Thus, with the present invention, for a given thread size a smaller andlighter nut can be utilized, or a stronger nut can be utilized, all tothe benefit of the end user.

By eliminating the crimping operation, the present invention also avoidsthe necessity for the crimped flange or more load bearing threads can bebuilt into the nut body for the small overall nut height.

Rieke U.S. Pat. No. 3,316,338, granted Apr. 25, 1967, discloses aprevailing torque type self-locking nut (hereinafter sometimes "theRieke nut") in which an internally threaded metallic nut body isprovided with an annular recess located axially adjacent one end of thenut thread. An annular groove is pierced in the recess to provide adouble undercut-like configuration. The radial nut surface adjacent therecess is knurled to provide better adherence of a locking element. Abolt having a thread and a smooth shank which corresponds to the corediameter of the nut thread is turned into threaded engagement with thenut thread, with the smooth shank in registry with the recess. Thisassembly is then dipped in plastic powder, so that the recess is filledwith powder which is also mounded up along the bolt shank. Thereafterthe bolt-nut assembly, with powder, is placed on a heating plate tocarry out a fusing process by heating the same to the melting point ofthe powder which is thereby fused into a unitary body said to be firmlybonded to the nut body after cooling and solidification. After cooling,the bolt is unscrewed from the nut in the direction such that the shanktraverses the nut thread. The cooled plastic material, which extendsover the face of the nut body, is said to form a unit with the nut.

The nut body of the Rieke nut is complex and therefore expensive tomanufacture, especially due to the necessity for piercing the doubleundercut groove in the recess. Also, it is noted that the radialdimension of the recess is quite large, resulting in a locking elementwhich has a ratio of axial length to radial thickness, apparently notgreater than about 1, which is on the same order of magnitude as theratio of the axial length to radial thickness of the pre-formed collarof the Sauer nut.

With the disclosed method of making the Rieke nut, it is impossible toprevent the plastic locking element from extending over the adjacentface of the nut body. Furthermore, such method is not adaptable to massproduction techniques.

Newnom U.S. Pat. No. 3,975,787, granted Aug. 24, 1976, discloses aprevailing torque type self-locking nut (hereinafter sometimes "theNewnom nut") having a standard metallic nut body having acircumferentially uninterrupted internal screw thread. The self-lockingfeature is derived from a ring-like plastic patch having acircumferential extent of greater than 180° adhered to the thread of thenut body. The Newnom nut is satisfactory for applications which do notrequire the performance capabilities of the Sauer nut. The Newnom nut ismade by a method which involves seating the nut body, either end first,on a pin a tapered portion of which cooperates with thecircumferentially uninterrupted thread to define a cavity into whichpowder of the plastic material is inserted. The nut body is then heatedto melt the powder.

It is therefore an important object of the present invention to providea prevailing torque type self-locking nut which is of significantlylower cost than the Sauer nut but which is at least as good as the Sauernut as to all significant performance criteria.

It is another object to provide a prevailing torque type self-lockingnut having a nut body provided with a circumferentially uninterruptedinternally threaded portion and a well portion surmounting the threadedportion and a locking element of thermoplastic material in the wellportion and bonded to the wall thereof.

It is a further object to provide a prevailing torque type self-lockingnut which is not subject to the dimensional limitations required of theSauer nut or the Rieke nut.

It is an additional object to provide a method of making a prevailingtorque type self-locking nut, which method is simple and inexpensive andat the same time reliable and readily adaptable to mass productiontechniques.

Additional objects are to provide a pin which is useful in carrying outthe method and a nut body which is a component of the self-locking nutand which can be produced, as by cold forming, at reduced cost relativeto the nut body of the Sauer nut.

SUMMARY OF THE INVENTION

In its article aspect, the present invention is a prevailing torque typeself-locking nut which comprises a one-piece metallic nut body and aradially thin self-locking element of thread impressionablethermoplastic material.

The nut body has first and second opposite ends and contains an internalscrew thread of predetermined pitch, predetermined nominal thread heightand predetermined fundamental triangle height H, and is located betweenthe first and second ends of the body. The thread itself has a firstaxial end adjacent the first end of the body and adapted to be enteredby a mating externally threaded member.

The nut body further has a well portion which extends axially from thesecond end of the body toward the thread. The well portion has aninternal surface, which in the illustrated embodiments is cylindrical.The internal surface faces the thread axis and is spaced therefrom adistance which is greater than one-half the major thread diameter. Inthe illustrated embodiments, the last-mentioned distance is not greaterthan about 105% of one-half the major thread diameter.

The self-locking element is in the well portion and has an externalsurface secured by adhesion to the internal surface of the well portionand an internal surface which confronts the thread axis and is spacedtherefrom a distance which is less than one-half the major threaddiameter and which in the illustrated embodiments is just slightly lessthan one-half the minor thread diameter.

Preferably, the axial end of the self-locking element remote from thethread is substantially axially coincident with the second end of thenut body and thus the locking element does not overlap the second end ofthe nut body, or vice versa.

Also, in the illustrated embodiments the internal surface of the wellportion is cylindrical and the external and internal surfaces of theself-locking element are cylindrical, so that the latter is in the formof a thin-walled bushing, tube or sleeve.

The axial length of the self-locking bushing is greater than twice thepitch of the thread and the ratio of the axial length of theself-locking bushing to its radial thickness is at least 2.5. In theillustrated embodiments, this ratio is 3.4 or more.

The radial thickness of the self-locking bushing is quite small, beingnot greater than the fundamental triangle height H.

In Paragraph 6.13, HANDBOOK H28 (1969) SCREW-THREAD STANDARDS FORFEDERAL SERVICES, issued March 1970 by the National Bureau of Standards(SD Catalog No. C13.11:28) defines "Fundamental Triangle Height",designated "H", as follows: "The fundamental triangle height of athread, that is, the height of a sharp-V thread, is the distance,measured radially, between the sharp major and minor cylinders orcones."

The inventive method is carried out with the aid of a pin. The pin has anut body support surface of greater transverse dimension than thethread, a cylindrical sealing portion of diameter just small enough tobe received within the thread, a cylindrical cavity-defining portioncoaxial with and of smaller diameter than the sealing portion and anannular sealing shoulder facing in generally the same direction as thenut body support surface and joining the cylindrical portions.

In the performance of the method, the nut body is placed, its first endfirst, on the pin until such first end rests on the nut body supportsurface and the sealing portion is within the thread and thecavity-defining portion is within the well portion, to establishtherewith an upwardly-facing cavity open at the second end of the nutbody. Powder of the thermoplastic material is deposited in the cavityand thereafter heated until all of it has become molten and is a unitarymass in wetting contact with the internal surface of the well portionbut spaced radially outwardly of the location occupied by thecavity-forming portion of the pin. Thereupon the nut body is cooled sothat the thermoplastic material solidifies, to provide the desiredself-locking element having an external surface bonded to the internalsurface of the well portion of the nut body and an internal surfaceconfronting the thread axis and spaced therefrom a distance less thanone-half the major thread diameter. At an appropriate time after thepowder starts to melt, the nut body is removed from the pin in thedirection opposite that in which the nut body was placed on the pin.

More specifically, the powder depositing step is accomplished bydropping powder into the cavity completely to fill the cavity. Duringthe powder depositing step, an excess of powder is deposited on thesecond end of the nut body and such excess is removed prior to theheating step.

The heating step is carried out by passing the assembly of the nut bodyand the pin between a pair of induction heating coils, thus to causethat powder which is adjacent to the internal surface of the wellportion to be the first powder to melt and the melting to proceed thenceradially inwardly toward the thread axis.

DESCRIPTION OF THE DRAWING

The invention will be described with reference to the accompanyingdrawing in which:

FIG. 1 is an axial sectional view of a prior art self-locking nut astaught by Sauer U.S. Pat. No. 2,450,694;

FIG. 2 is a plan view of a first nut embodying the invention, comprisinga nut body and a locking bushing;

FIG. 3 is a view on line 3--3 of FIG. 2;

FIG. 4 is a plan view of a second nut embodying the invention,comprising a nut body and a locking bushing;

FIG. 5 is a view on line 5--5 of FIG. 4;

FIG. 6 is an enlarged fragmentary view showing in axial section, a nutbody as in FIGS. 2 and 3, and, in axial elevation, a pin, the nut bodymounted on the pin, with powder of thermoplastic material filling acavity between the nut body and the pin;

FIG. 7 is a view similar to FIG. 6 but showing the completed nut ofFIGS. 2 and 3 and further showing the dimensional relationships amongthe nut body, the bushing and the pin;

FIGS. 8 through 11 are views showing in axial section, the nut body ofFIGS. 2, 3, 6 and 7 and in fragmentary axial elevation, the pin of FIGS.6 and 7, these views depicting in sequence a series of steps in themanufacture of the nut of FIGS. 2 and 3;

FIG. 12 is a view similar to FIG. 6 but showing a modified nut body andmodified pin;

FIG. 13 is a view similar to FIG. 7 but showing a first modifiedcompleted nut which may be made from the nut body of FIG. 12 with theaid of the pin of FIG. 12 and further showing for the first modifiedcompleted nut the dimensional relationships among the bushings, the nutbody and the pin; and

FIG. 14 is a view similar to FIG. 13 but showing a second modifiedcompleted nut which may be made from the nut body of FIG. 12 with theaid of the pin of FIG. 12 and further showing for the second modifiedcompleted nut the dimensional relationships among the bushing, the nutbody and the pin.

DESCRIPTION OF THE INVENTION

FIG. 1 shows, in axial section, a prior art nut 12, as taught by SauerU.S. Pat. No. 2,450,694 and over which the present invention is animprovement. Nut 12 is of the prevailing torque type and comprises aone-piece metallic nut body 14 having a threaded bore portion 16. Afirst end 18 of nut 12 and of bore portion 16 is adapted to be enteredby a mating externally threaded member (not shown). At a second end 20of threaded bore portion 16 is an annular recess or well 22 formed inpart by a circumferentially continuous annular flange portion 24 whichextends axially away from first end 18 and which includes a cylindricalsurface 26 coaxial with and confronting the axis of threaded boreportion 16. Nut body 14 further has an annular countersunk shoulder 27facing away from end 18 and joining surface 26 and second end 20 ofthreaded portion 16.

Prior art nut 12 also includes a pre-formed (as by injection molding)nylon locking collar 28 mechanically held in recess 22. Flange portion24 is crimped so as to be in engagement with upper surface 30 of collar28, thus to retain the same in recess 22 and prevent the same fromturning relative to body 14. Resistance of collar 28 to turning may beaided by staking the portion of flange portion 24 overlying collar 28 atpredetermined locations, as shown at 32. Collar 28 has an internalcylindrical surface 34 which is coaxial with and confronts the axis ofthreaded bore portion 16 and which has a diameter which is somewhat lessthan the major thread diameter, so that continued rotation of theexternally threaded member, after it traverses threaded bore portion 16,will cause it to engage cylindrical surface 34 of collar 28, to impressa thread therein and achieve the desired self-locking effect, all inknown fashion. Since collar 28 is preformed, it tends to have a sharpcorner 35 at the axial end of surface 34 adjacent threaded bore portion16.

FIGS. 2, 3, 7 and 11 show a first preferred nut 36 embodying the presentinvention. Nut 36 comprises a one-piece metallic nut body 38 having afirst end 40 providing nut 36 with a work clamping surface and a secondend 42 opposite and parallel to first end 40. Body 38 is also shown inFIGS. 6, 8, 9 and 10.

Body 38 also has a circumferentially uninterrupted internal screw thread44 of predetermined major and minor diameters, located between ends 40and 42. The axis of thread 44 is perpendicular to ends 40 and 42 and oneaxial end of thread 44 is adjacent end 40 of body 38, so as to beadapted to be entered by a mating externally threaded member.

Body 38 further has an annular countersunk shoulder 46 surrounding theaxis of thread 44 and facing away from end 40 at the other end of thread44 and a well portion 48 extending axially from second end 42 of body 38toward thread 44 and in open communication with end 42 and thread 44.Well portion 48 has an internal circumferentially and axially continuouscylindrical surface 50 coaxial with thread 44 and spaced from the threadaxis a distance greater than one-half the major thread diameter. Surface50 is of a predetermined axial extent and joins second end 42 of body 38and shoulder 46.

Nut 36 further includes a thin-walled self-locking bushing, tube orsleeve 52 of thread impressionable thermoplastic material, such asnylon, located in well portion 48 and having an externalcircumferentially continuous surface 54 secured by adhesion to surface50 throughout substantially the entire axial and circumferential extentthereof. Bushing 52 also has an internal circumferentially continuoussurface 56 confronting and substantially coaxial with the thread axisand spaced therefrom a distance less than one-half the major threaddiameter. The axial end of bushing 56 adjacent thread 44 may be slightlyflared outwardly in a bell-mouth like configuration, as shown at 58, asseen particularly in FIG. 7, to facilitate entry of a mating externallythreaded member into bushing 52.

Nut body 38 is also provided with hexagonal external wrenching surfaces60 equidistant from the thread axis and extending axially throughout amajor portion of the axial length of body 38. Wrenching surfaces 60define a hexagonal wrenching configuration of predetermined standardacross-the-flats-dimension.

Body 38 also has an external conical surface 62 coaxial with thread 44and joining end 42 and wrenching surfaces 60 and providing a visualindication distinguishing end 40 from end 42 and also means whereby thenut can be properly oriented by automatic feeding equipment.

Nuts 36 of the 5/8-18 thread size have been made by the hereinafterdisclosed method and successfully tested.

The following parameters apply to such nuts 36 of the 5/8-13 threadsize:

TABLE 1 Nut 36 of 5/8-18 Thread Size

Overall nut height (distance from surface 40 to surface 42)--0.760 inch;

Nut height (from surface 40 to surface 42)--0.606 inch;

Height of surface 50 and axial length of bushing 52--0.154 inch;

Diameter of nut body surface 50--0.641 to 0.648 inch;

Diameter of bushing surface 56--0.557 to 0.569 inch;

Radial thickness of bushing 52--0.036 to 0.046 inch;

Minor diameter of thread 44--0.571 to 0.579 inch;

Major diameter of thread 44--0.625 inch minimum;

Countersunk shoulder 46--170° included angle;

Across-the-flats dimension of wrenching surfaces 60--0.928 to 0.940inch; and

Weight per 100 pieces--9.5 pounds.

By way of comparison, the following parameters apply to a correspondinghexagonal commercial prior art nut 12 of the 5/8-18 inch thread size:

TABLE 2 Prior Art Nut 12 of 5/8-18 Thread Size

Overall nut height--0.750 inch;

Nut height (from end 18 to surface 26)--0.596 inch;

Diameter of surface 26--0.828 inch;

Diameter of surface 34--0.552 inch minimum (and in most instances aboutsame as minor diameter of thread);

Minor diameter of thread--0.571 to 0.579 inch;

Major diameter of thread--0.625 inch minimum;

Countersunk shoulder 27--170° included angle;

Across-the-flats dimension of hexagonal wrenching surfaces--0.928 to0.940 inch; and

Weight per 100 pieces--8.9 pounds.

In the manufacture of prior art nut 12, during the crimping of flangeportion 24 into engagement with the upper surface 30 of collar 28, thelatter is somewhat deformed. Prior to assembly with body 14, pre-formedcollar 28 has inner and outer coaxial cylindrical surfaces and upper andlower plane parallel surfaces perpendicular to the upper and lowersurfaces. Initially, the dimensions of collar 28 for the commercialprior art nut 12 of the 5/8-18 thread size are as follows:

TABLE 3 Collar 28 of Prior Art Nut 12 of 5/8-18 Thread Size

Diameter of inner surface (which becomes surface 34)--0.583 to 0.589inch;

Diameter of outer surface (which confronts surface 26)--0.813 to 0.817inch;

Radial thickness--0.112 to 0.117 inch;

Distance from upper surface to lower surface--0.135 to 0.145 inch.

FIGS. 4 and 5 show a second preferred nut 66 embodying the presentinvention. Nut 66 takes advantage of the fact that the present inventioninvolves no deformation of metal after the locking element is in place,as will be explained in greater detail below.

Nut 66 comprises a one-piece metallic nut body 68 having a first end 70having an external cylindrical flange 71, providing nut 66 with a workclamping surface and a second end 72 opposite and parallel to first end70. Flange 71 is quite thin in the axial direction.

Body 68 also has a circumferentially uninterrupted internal screw thread74 of predetermined major and minor diameters, located between ends 70and 72. The axis of thread 74 is perpendicular to ends 70 and 72 and oneaxial end of thread 74 is adjacent end 70 of body 68, so as to beadapted to be entered by a mating externally threaded member.

Body 68 further has an annular countersunk shoulder 76 surrounding theaxis of thread 74 and facing away from end 70 at the other end of thread74 and a well portion 78 extending axially from second end 72 of body 68toward thread 74 and in open communication with end 42 and thread 74.Well portion 78 has an internal circumferentially and axially continuouscylindrical surface 80 coaxial with thread 74 and spaced from the threadaxis a distance greater than one-half the major thread diameter. Surface80 is of a predetermined axial extent and joins second end 72 of body 68and shoulder 76.

Nut 66 further includes a thin-walled self-locking bushing, tube orsleeve 82 of thread impressionable thermoplastic material, such asnylon, located in well portion 78 and having an externalcircumferentially continuous surface 84 secured by adhesion to surface80 throughout substantially the entire axial and circumferential extentthereof. Bushing 82 also has an internal circumferentially continuoussurface 86 confronting and substantially coaxial with the thread axisand spaced therefrom a distance less than one-half the major threaddiameter. The axial end of bushing surface 86 adjacent thread 74 may beslightly flared outwardly in a bell-mouth like configuration (in themanner shown at 58 in FIG. 7 for bushing 52), to facilitate entry of amating externally threaded member.

Nut body 68 is also provided with hexagonal external wrenching surfaces90 equidistant from the thread axis and extending axially throughout amajor portion of the axial length of body 68. Wrenching surfaces 50 to90 define a hexagonal wrenching configuration of predetermined standardacross-the-flats dimension, but smaller than that of nut body 38.

Body 68 also has an external conical surface 92 coaxial with thread 74and joining end 72 and wrenching surfaces 90 and providing a visualindication distinguishing end 70 from end 72 and also means whereby thenut can be properly oriented by automatic feeding equipment.

Nuts 66 of the 5/8-18 thread size have been made by the hereinafterdisclosed method and successfully tested.

The following parameters apply to such nuts 66 of the 5/8-18 threadsize:

TABLE 4 Nut 66 of 5/8-18 Thread Size

Overall nut height (distance from surface 70 to surface 72)--0.685 inch;

Nut height (from surface 70 to surface 80)--0.531 inch;

Height of surface 80 and axial length of bushing 82--0.154 inch;

Diameter of nut body surface 80--0.641 to 0.648 inch;

Diameter of bushing surface 86--0.557 to 0.569 inch;

Radial thickness of bushing 82--0.036 to 0.046 inch;

Minor diameter of thread 74--0.571 to 0.579 inch;

Major diameter of thread 74--0.625 inch minimum;

Countersunk shoulder 76--170° included angle;

Across-the-flats dimension of wrenching surfaces 90--0.865 to 0.877inch;

Outside diameter of flange 71--1.047 inches; and

Weight per 100 pieces--7.1 pounds.

It will be seen that the 5/8-18 nut 66 achieves a weight saving of about20% with respect to the 5/8-18 prior art nut 12. This weight saving ismade possible by the fact that the present invention involves no metaldeformation after the locking element is in place in the nut body, thuspermitting heat treatment of the nut body to increase its strength andreduce its size, primarily by utilizing a smaller, but still a standardsize hexagonal wrenching configuration.

Even without the strength consideration, the present invention makespossible significant weight saving (reduction of size of hexagonalwrenching configuration). In the 5/8-18 prior art nut 12, the 0.828 inchdiameter of surface 26 requires that the outer diameter of flangeportion 24 be 0.892 inch, which latter dimension must be less than theacross-the-flats dimension of the hexagonal wrenching configuration.Thus, it would be impossible to utilize in the 5/8-18 prior art nut 12the 0.865 to 0.877 inch across-the-flats dimension of the 5/8-18 nut of66 of the present invention, which is possible in the latter nut due tothe radial thinness of bushing 52.

Thus, the present invention has overcome a geometric limitation on thesize of the hexagonal wrenching configuration. So far as geometry isconcerned, with the present invention, it is merely necessary that theacross-the-flats dimension of the hexagonal wrenching configuration begreater than the diameter of surface 50 or 80.

Prior art nuts 12 of the 5/8-18 thread size and nuts 36 of the samethread size, and made by the hereinafter described method, have beensubjected to torque reuse tests in accordance with MilitarySpecification MIL-N-25027. Both passed with the following substantiallyequivalent results, all of which are in inch-pounds:

                  TABLE 6                                                         ______________________________________                                        Torque Reuse Tests                                                            ______________________________________                                        Prior Art Nut 12 of 5/8-18 Thread Size                                        Torque                                                                        Sample                                                                              1st On  1st Off 7th On 7th Off                                                                             15th On                                                                              15th Off                            ______________________________________                                        1     100     110     100    120   100    120                                 2      95     100     120    130    95     95                                 3     120     100      60     60    60     60                                 4     150     140     140    135   100    100                                 5     120     140     150    145   115    110                                 ______________________________________                                        Nut 36 of 5/8-18 Thread Size                                                  Torque                                                                        Sample                                                                              1st On  1st Off 7th On 7th Off                                                                             15th On                                                                              15th Off                            ______________________________________                                        1     140     160     120    140   60     75                                  2     100     140     100    140   90     110                                 3     150     150     110    120   50     60                                  4     135     115      95    100   45     44                                  5     120     120     110    130   110    90                                  6     120     140     100    115   70     70                                  7     120     120     140    140   75     75                                  ______________________________________                                         The MIL-N-25027 requirement for each "On" torque is 300 inch-pounds     maximum and for each "Off" torque is 32 inch-pounds minimum.

The method of the present invention will now be described as related tothe production of nut 36. In broad terms, the method utilizes powder ofthermoplastic material, such as nylon, which powder is placed withinsurface 50 of nut body 38 which is then heated to melt the powder. Uponcooling, the molten thermoplastic material solidifies to form thedesired bushing 52 strongly adhered to surface 50.

More particularly, the steps of the method are illustrated in FIGS. 6through 11. The method is carried out with the aid of a pin or mandrel100. Pin 100 is of a material to which the melted thermoplastic materialwill not adhere. Examples of suitable mandrel material are fluoroplasticresins, such as Teflon, as is well known.

Pin 100 has a bottom cylindrical portion 102 of predetermined diameter,an intermediate or sealing cylindrical portion 106 of smaller diameterthan bottom portion 102 and a top or cavity-defining cylindrical portion110 of smaller diameter than intermediate portion 108. Top cylindricalportion 110 has a rounded tip 112 at the axial end thereof remote fromportion 102.

Portions 102, 106 and 110 are coaxial and portions 102 and 106 arejoined by a plane annular shoulder or nut body support surface 104perpendicular to the axis of pin 100, while portions 106 and 110 arejoined by a plane annular shoulder or sealing surface 108, alsoperpendicular to the axis of pin 100. The intersection of portion 106and sealing surface 108 is abrupt, to provide a sharp cornertherebetween.

Pertinent dimensions of the pin 100 which was used in manufacturing nuts36 of the 5/8-18 thread size are as follows:

TABLE 7 Pin 100 For Nut 36 Of 5/8-18 Thread Size

Diameter of bottom portion 102 and outer diameter of nut support surface104--0.812 inch;

Diameter of intermediate portion 106 and outer diameter of sealingsurface 108--0.562 inch;

Diameter of top portion 110--0.477 to 0.483 inch;

Axial length of intermediate portion 106--0.596 inch;

Axial length of top portion 110--0.194 inch;

Combined axial length of portions 106 and 110--0.790 inch; and

Radius of rounded tip 112--0.060 inch.

Nut body 38 is placed on pin 100, with the axis of pin 100 vertical,until end 40 rests on nut body support surface 104, and the axis ofthread 44 is substantially coincident with the axis of pin 100. Withbody 38 and pin 100 thus assembled, the following relationships appear:intermediate portion 106 is within thread 44 with a radial clearance ofabout 0.004 to about 0.008 inch therebetween; sealing surface 108 liesin a plane which is about 0.01 inch below the plane of the end ofsurface 50 adjacent thread 44; and the axial end of pin 100 remote fromportion 102 lies in a plane which is about 0.030 inch above surface 42.

Nut body 38 and pin 100 cooperate to provide an annular cavity 114 whichis open at end 42 of nut body 38.

More particularly, cavity 114 is defined by surface 50, the upper end ofthread 44 and shoulder 46 of nut body 38 and by top cylindrical portion110 and sealing surface 108 of pin 100. Cavity 114 has a radialdimension of about 0.080 to 0.084 inch.

With body 38 assembled with pin 100 as aforesaid, these parts are passedunder a powder supply tube 116 (FIG. 8) which provides a constantlyflowing stream 118 of powder of the thermoplastic material, thus todeposit powder in cavity 114 until it is completely filled. During suchdepositing an excess amount of powder may be deposited on surface 42 ofbody 38 and on the end of pin 100 remote from portion 102. Sealingsurface 108 prevents any substantial amount of powder from falling outthe bottom of cavity 114.

Any such excess powder is removed by passing the body 38-pin 100assembly beneath a hood 124 in the form of an inverted funnel and whichsubjects the cavity end of the assembly to a puff of air 122, all asshown in FIG. 9.

Removal of excess powder may also be aided by brushing upper end of thebody 38-pin 100 assembly with a felt wiper (not shown) after powderdeposition (FIG. 8) and prior to subjecting the assembly to the puff ofair 122.

After removal of excess powder, the situation is as best shown in FIG.6, with powder completely filling cavity 114 as shown at 120 andpossibly slightly running up onto rounded tip 112 of pin 100.

Next, the body 38-pin 100 assembly is passed between a pair of parallelinduction heating elements 126 which are located close to body 38 in theaxial vicinity of top portion 110 of pin 100, as shown in FIG. 10.Heating elements 126 heat body 38 to a temperature sufficiently high tomelt powder 120. The first powder to melt is that in contact withsurface 50. The melting proceeds thence inwardly until all of powder 120has been melted. When powder of thermoplastic material is melted andthen solidified, the volume of solidified thermoplastic material issubstantially less than that previously occupied by the powder. Forrough purposes, it may be deemed that the solidified material occupiesabout one-half the volume previously occupied by the powder. Because themelting of powder 120 proceeds from the outside in, the surface tensionof the molten thermoplastic material adjacent surface 50 drawsadditional thermoplastic material which is located immediately inwardlyof the already molten thermoplastic material into the molten mass, andso on until all of powder 120 has become molten, and the molten materialis a unitary mass in wetting contact with surface 50 but spaced radiallyoutwardly of the location occupied by portion 110 of pin 100.

Upon subsequent cooling, the thermoplastic material within surface 50solidifies, thus to provide the desired self-locking bushing 52 stronglyadhered to surface 50. FIG. 7 shows the dimensional relationshipsbetween bushing 52 and pin 100. It is also noted that, due to thesurface tension of the molten thermoplastic powder, the axial ends ofbushing surface 56 may become slightly flared outwardly, providing ameniscus-like contour.

At an appropriate time after powder 120 starts to melt, nut 36 isremoved from pin 100, as indicated in FIG. 11.

The axial end of bushing 52 remote from thread 44 is axially coincidentwith end 42 of nut body 38, thus overcoming the dimensional restrictionswhich are inherent in prior art nut 12 due to the crimped flange portionof the latter.

Adherence of the bushing to the nut body may be enhanced by gritblasting surface 50 to provide up to 31/2 times the original surfacearea, by applying a chromate or an iron phosphate conversion coating (40to 90 mg/square foot) to provide protection against infusion of wateralong the bond line between nut body 38 and bushing 52, applying aprimer (such as an epoxy) to surface 50, and/or by utilizing a type ofnylon powder in which a primer is incorporated. An example of the latteris available from Thermoclad Company, 4688 Iroquois Ave., Erie, Penn.15511, under the designation "DURALON JM". DURALON JM is a nylon powderwhich incorporates a primer. The particle size is approximately asfollows:

5% coarser than 80 mesh;

45% 80 to 200 mesh; and

50% finer than 200 mesh.

An important consideration is the tendency of the molten thermoplasticmaterial to sag, i.e., to become concentrated at the bottom of cavity114 before it has had an opportunity to solidify. If sagging is severeenough, the result is an unsatisfactory product.

It has been found that the sagging problem can be avoided if the ratioof the axial length of bushing 52 or 82 to its radial thickness is quitelarge. More particularly, if that ratio is at least about 2.5, saggingis generally not a problem. For the 5/8-18 nuts 36 and 66, dimensionedas above, the ratio can vary between about 3.4 and 4.3.

From the foregoing dimensions of collar 28 of the 5/8-16 prior art nut12, it can be seen that the maximum value of the ratio of the axiallength of collar 28 to its radial thickness is about 1.3.

The diameter of bushing surface 56 or 86 is largely predetermined by thedesired locking action of the nut, as is the axial length of bushing 52or 82, that axial length being on the order of magnitude of severalthread pitches. To maximize the ratio of the axial length of bushing 52or 82 to its radial thickness, the diameter of surface 50 or 80 ischosen to be as small as possible, just large enough so that theintegrity of the bond of bushing surface 54 or 84 to nut body surface 50or 80 is not destroyed when the external thread of a complementarymember traverses and impresses a thread in bushing 52 or 82.

For the 5/8-18 nuts 36 and 66, dimensioned as above, the diameter ofsurfaces 50 and 80 is 103% of the nominal major thread diameter. Inother nuts 36 and 66, the diameter of surfaces 50 and 80 may be up to105% of the nominal major thread diameter.

Other techniques for alleviating the sagging problem include theincorporation of a thixotropic agent (such as silica or mica particles)in the thermoplastic powder, inverting the nut while it is coolingand/or accelerating cooling by quenching in an oil bath.

It is to be understood that the use herein of the term "thermoplasticmaterial" is broad enough to include such material containing additives,such as primers and thixotropic agents.

Other modifications which might be used to enhance retention of thebushing include making surface 50 or 80 ellipsoidal (to provide partialthread engagement along the minor axis of the ellipse or not);interrupting surface 50 or 80 with thread segments extending to nut bodyend 42 or 72; roughening surface 50 or 80 by providing the same withshallow corrugations, flutes or splines; or providing surface 50 or 80with a reverse taper, as by staking nut body end 42 or 72 while nut body38 or 68 is being formed.

To revert to the hereinabove disclosed method, several seconds arerequired for powder 120 to become completely molten after body 38-pin100 assembly passes heating elements 126. It has been found that it ispossible to remove body 38 from pin 100 at any time after melting issubstantially underway but before it is complete, with no adverse effecton the finished product. It is even more unnecessary for body 38 toremain on pin 100 until the thermoplastic material completelysolidifies. Hence, the parts may never be physically related as shown inFIG. 7.

Some users of prevailing torque type self-locking nuts havespecifications therefor, which specifications include maximumdimensional limitations for axial nut length, often making nodimensional provision for the inclusion of a self-locking elementsurmounting the nut thread.

Substantial reductions in the axial length of nuts embodying theinvention can be achieved by utilizing the techniques illustrated inFIGS. 12, 13 and 14.

FIGS. 13 and 14 show first and second modified nuts 128 and 130,respectively, embodying the invention. Each of nuts 128 and 130 includesa modified one-piece metallic nut body 132 (FIGS. 12, 13 and 14). Nut128 further includes a thin-walled self-locking bushing, tube or sleeve134 of thread impressionable thermoplastic material, such as nylon, andnut 130 further includes a thin-walled self-locking bushing, tube orsleeve 136. Bushings 134 and 136 differ only as to their internalconfigurations, as described hereinafter.

Modified nut body 132 has a first end (not shown) providing a workclamping surface, a second end 138 and a circumferentially uninterruptedinternal screw thread 140 of predetermined major and minor diameters andpredetermined pitch located between the work clamping surface and end138. The axis of thread 140 is perpendicular to the work clampingsurface and end 138 and one axial end of thread 140 is adjacent the workclamping surface, so as to be adapted to be entered by a matingexternally threaded member. Nut body 132 further has a well portion 142extending axially from second end 138 toward thread 140 and in opencommunication with end 138 and thread 140. Well portion 142 has aninternal circumferentially and axially continuous cylindrical surface144 coaxial with thread 140 and spaced from the thread axis a distancegreater than one-half the major thread diameter. Surface 144 joinssecond end 138 and extends therefrom a predetermined axial distancetoward thread 140. The last-mentioned axial distance may be on the orderof magnitude of one thread pitch.

The axial end of cylindrical surface 144 remote from end 138 intersectsa countersunk surface 146 coaxial with surface 144 and having apredetermined conical angle, which for nut body 132 is about 60°. Thread140 runs out on countersunk surface 146.

The diameter of surface 144 and the magnitude of the conical angle ofsurface 146 are such that surface 146 interrupts thread 140 over anaxial distance which may be on the order of magnitude of one threadpitch, or slightly greater.

The diameter of surface 144 may be between about 101% and about 105% ofthe major thread diameter.

FIGS. 12, 13 and 14 show nut body 132 mounted on a pin 148, which is ofa material to which the melted thermoplastic material used for lockingelements 134 and 136 will not adhere. Pin 148 has a bottom cylindricalportion (not shown) of predetermined diameter and providing a nut bodysupport surface, an intermediate or sealing cylindrical portion 150 ofsmaller diameter than the bottom portion and a cavity-defining portion152 which has a rounded tip 154 at the axial end thereof remote fromportion 150.

Cavity-defining portion 152 is defined in part by a frusto-conicalelement 156 coaxial with and axially joining and extending fromcylindrical portion 150. Element 156 is of maximum diameter at itscircle of juncture with portion 150. Cavity-forming portion 152 isfurther defined by a cylindrical element 158 coaxial with element 156and axially extending from the end of element 156 to rounded tip 154.

The diameter of cylindrical portion 150 is slightly less than the minorthread diameter, and is such that portion 150 can be freely received,but just barely so, within thread 140.

The conical angle of frusto-conical element 156 may be about 30° and itsaxial length, between its circle of juncture with cylindrical portion150 and its circle of juncture with cylindrical element 158, may bebetween one and one-half and two thread pitches.

Nut body 132 is placed on pin 148, with the axis of pin 148 vertical,until the work clamping surface rests on the nut body support surface ofpin 148, and the axis of thread 140 is substantially coincident with theaxis of pin 148. With nut body 132 and pin 148 thus assembled, it shouldbe noted that the plane of the circle of juncture of frusto-conicalelement 156 and cylindrical element 158 may coincide or nearly coincidewith the plane of the circle of juncture of countersunk surface 146 andthe cylinder of the minor thread diameter. The axial length ofcylindrical element 158 is such that the axial end of element 158 remotefrom element 156 lies in a plane slightly above second end 138 of nutbody 132.

Nut body 132 and pin 148 cooperate to provide an annular cavity 160(FIG. 12) which is open at end 138 of nut body 132. More particularly,cavity 160 is defined by surface 144, surface 146, the portion of thread140 confronting frusto-conical element 156, frusto-conical element 156and cylindrical element 158.

With body 132 assembled with pin 148, cavity 160 is filled with powderof the thermoplastic material as shown at 162 in FIG. 12, in previouslydescribed fashion. Next, the body 132-pin 158 assembly is passed betweena pair of induction heating elements which heat body 132 to atemperature sufficiently high to melt powder 162, thus to become aunitary mass in wetting contact with surface 144, surface 146 and theadjacent portion of thread 140.

Upon subsequent cooling, the thermoplastic material within body 132solidifies, thus to provide bushing 134 (FIG. 13) or 136 (FIG. 14),having an external surface secured by adhesion to surface 144, surface146 and the full thread 140 axially adjacent surface 146, as indicatedat 140a. The axial extent of bushing 134 or 136 on the full thread 140is, as shown, somewhat greater than one thread pitch. The portion of thebushing adhered to thread 140 may be circumferentially continuous, as isthe case with nuts 128 or 130, or it may be circumferentially limited.In the latter event, the portion of the bushing on thread 140 may be inthe form of at least one axially extending finger.

Nut 128 or 130 may be plated, as with cadmium, after formation ofbushing 134 or 136. Such plating should be carried out in an acidicplating bath, since it has been found that if an alkaline bath, such ascyanide, is used the adhesion of the self-locking element to the nutbody is adversely affected. Surprisingly, with an acidic plating bath,such adhesion is not affected.

It is to be noted that bushing 134 (FIG. 13) has an inner surface 164confronting the nut axis and spaced therefrom a distance less thanone-half the major diameter of thread 140. More particularly, innersurface 164 is spaced from the nut axis a distance which is less thanone-half the minor diameter of thread 140. It is also to be noted thatthe portion of inner surface 164 axially adjacent end 138 is somewhatconvex, due to slight sagging during cooling of the thermoplasticmaterial. The portion of inner surface 164 axially remote from end 138in general follows the contour of thread 140 and is slightly outwardlyflared at the axial end of bushing 134 which is entered by a matingexternally threaded member.

It is to be noted that bushing 136 (FIG. 14) has an inner surface 166confronting the nut axis and spaced therefrom a distance less thanone-half the major diameter of thread 140. More particularly, innersurface 166 is spaced from the nut axis a distance which is less thanone-half the minor diameter of thread 140. It is also to be noted thatthe portion of inner surface 166 axially adjacent end 138 issubstantially cylindrical. The portion of inner surface 166 axiallyremote from end 138 in general follows the contour of thread 140 and isslightly outwardly flared at the axial end of bushing 136 which isentered by a mating externally threaded member.

Both nut 128 and nut 130 were made using a thermoplastic powder whichwas a mixture of DURALON JM nylon 11 powder and epoxy, the latter beingintroduced to enhance adhesion of the bushing to the nut body. Variousratios of epoxy to total weight of the mixture have been tried. It hasbeen found that if the ratio is 15% or greater, the bushing will exhibitundesirable fissuring, which leaves something to be desired from thestandpoint of appearance.

For nuts 128 and 130, the ratio of the axial length of that portion ofthe self-locking element which is within well portion 142 to the radialthickness of that portion is substantialy less than 2.5. For thatcondition, it has been found that if DURALON JM nylon 11 powder alone isused for the self-locking element, sagging is a problem. However, it hasbeen discovered that if the ratio of epoxy to total weight of themixture is greater than about 31/2%, the results are surprising as tothe sagging problem. Epoxy alone sags significantly, but when said ratiois greater than 31/2%, sagging is much less than when either is usedalone.

Accordingly, the preferred range for said ratio is between 31/2% and 15%and a particularly preferred ratio is about 71/2%.

In any event, the mixture which was used to make nuts 128 and 130 wasabout 10% epoxy and 90% DURALON JM nylon 11 powder.

In the fabrication of nut 128, nut body 132 was maintained in an uprightposition during cooling, whereas in the fabrication of nut 130, nut body132 was inverted during cooling. This difference in processing accountsfor the difference between the contours of bushing surfaces 164 and 166,that of the latter being slightly preferable to that of the former.

By following the techniques of FIGS. 12, 13 and 14, it has been possibleto reduce axial nut length by about 11/2 to 2 pitches.

The parts may never be physically related as shown in FIGS. 13 and 14,for the same reason given in the foregoing discussion of FIG. 7.

The foregoing description of the invention is by way of example only,the scope of the invention being defined by the following claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are as follows:
 1. A method of making a prevailingtorque type self-locking nut by producing a locking bushing of threadimpressionable thermoplastic material in a metallic nut body havingfirst and second opposite ends, an internal screw thread ofpredetermined nominal major and minor diameters between said ends and awell portion extending axially from said second end toward said threadand in open communication with said second end and with said thread,said well portion having a circumferentially continuous cylindricalinternal surface coaxial with and facing the nut thread axis and ofdiameter greater than one-half the major thread diameter, said methodbeing carried out with the aid of a pin having a nut body supportsurface, a cylindrical sealing portion of diameter just small enough tobe received within said thread, a cylindrical cavity-defining portioncoaxial with and of smaller diameter than the sealing portion and anannular sealing shoulder facing in generally the same direction as saidnut body support surface and joining said cylindrical portions, saidmethod comprising the steps of placing said nut body, said first endfirst, on said pin until said first end rests on said nut body supportsurface, said sealing portion is within said thread and saidcavity-defining portion is at least partly within the well portion ofsaid nut body to establish with the internal surface of the well portionan upwardly-facing annular cavity completely surrounding the thread axisand open at said second end of said body, depositing powder of saidthermoplastic material in said cavity by dropping powder into saidcavity completely to fill the cavity, thereafter heating the sodeposited powder until all of it has become molten and is a unitary massin wetting contact with said internal surface of said well portionthroughout the circumference and axial extent thereof but is spacedradially outwardly of the location occupied by the cavity-definingportion of said pin, cooling said nut body so that the thermoplasticmaterial solidifies, to provide said locking bushing having acylindrical external surface secured by adhesion to said internalsurface of said well portion and an internal surface confronting andsurrounding and substantially coaxial with the thread axis and spacedtherefrom a distance less than one-half the major thread diameter andremoving the nut from the pin in the direction opposite that in whichthe nut body was placed on the pin after the powder starts to melt. 2.The invention of claim 1 also including the step of inverting the nutbody during the cooling step.
 3. The invention of claim 1 wherein thecooling step is accelerated by quenching.
 4. The invention of claim 1wherein during the powder depositing step an excess of such powder isdeposited on the second end of said nut body and said method comprisesthe additional step of removing such excess prior to the heating step.5. The invention of claim 1 wherein the heating step is accomplished bypassing the assembly of the nut body and the pin between a pair ofinduction heating coils, thus to cause that powder which is adjacent tosaid internal surface of said well portion to be the first powder tomelt and the melting to proceed thence radially inwardly.
 6. Theinvention of claim 1 wherein said powder comprises a mixture ofparticles of said thermoplastic material and epoxy, the ratio by weightof epoxy to total mixture weight having a lower limit of 31/2%.
 7. Theinvention of claim 6 wherein said ratio has an upper limit of less than15%.
 8. The invention of claim 6 wherein said ratio is about 71/2%.
 9. Amethod of making a prevailing torque type self-locking nut by producinga locking element of thread impressionable thermoplastic material in ametallic nut body having an internal thread having an axis and a wellportion extending axially from said thread and said well portion havingan internal surface facing the thread axis, said method comprising thesteps of depositing powder of said thermoplastic material in said wellportion with said well portion facing generally vertically upwardly,heating the so deposited powder so that it becomes a unitary molten massin wetting contact with said internal surface and then cooling saidmolten thermoplastic material to solidify same and during said coolingstep inverting said nut body, thus to provide said locking elementhaving an external surface secured by adhesion to said internal surfaceof said well portion and an internal surface confronting the thread axisand positioned to be traversed by an external thread.
 10. The inventionof claim 9 wherein the cooling step is accelerated by quenching.
 11. Theinvention of claim 9 wherein said powder comprises a mixture ofparticles of said thermoplastic material and epoxy, the ratio by weightof epoxy to total mixture weight having a lower limit of 31/2%.
 12. Theinvention of claim 11 wherein said ratio has an upper limit of less than15%.
 13. The invention of claim 11 wherein said ratio is about 71/2%.